package com.example.utils;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;


/**
 * @author Boomp
 * @date 2020/2/28 18:47
 * TODO:
 */


public class MD5<psvm> {
    protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6','7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    protected static MessageDigest messageDigest = null;
    static {
        try {
            messageDigest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException nsaex) {
            System.err.println(MD5.class.getName()+"初始化失败，MessageDigest不支持MD5!");
            nsaex.printStackTrace();
        }
    }


    public static void main(String[] args) throws IOException {
//        long begin = System.currentTimeMillis();
//
//
//        File big = new File("文件绝对路径");
//        String md5 = getFileMD5String(big);
////String md5 = getMD5String("a");
//        long end = System.currentTimeMillis();
//        System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000) + "s");
        File file =new File("D:\\周瑞.zip");

       String s= MD5.getFileMD5String(file);
        System.out.println(s);
    }



    public static String getFileMD5String(File file) throws IOException {
        FileInputStream in = new FileInputStream(file);
        FileChannel ch = in.getChannel();

        //700000000 bytes are about 670M
        int maxSize=700000000;

        long startPosition=0L;
        long step=file.length()/maxSize;

        if(step == 0){
            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0,file.length());
            messageDigest.update(byteBuffer);
            return bufferToHex(messageDigest.digest());
        }

        for(int i=0;i<step;i++){
            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition,maxSize);
            messageDigest.update(byteBuffer);
            startPosition+=maxSize;
        }

        if(startPosition==file.length()){
            return bufferToHex(messageDigest.digest());
        }


        MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition,file.length()-startPosition);
        messageDigest.update(byteBuffer);


        return bufferToHex(messageDigest.digest());
    }


    public static String getMD5String(String s) {
        return getMD5String(s.getBytes());
    }


    public static String getMD5String(byte[] bytes) {
        messageDigest.update(bytes);
        return bufferToHex(messageDigest.digest());
    }


    private static String bufferToHex(byte bytes[]) {
        return bufferToHex(bytes, 0, bytes.length);
    }


    private static String bufferToHex(byte bytes[], int m, int n) {
        StringBuffer stringbuffer = new StringBuffer(2 * n);
        int k = m + n;
        for (int l = m; l < k; l++) {
            appendHexPair(bytes[l], stringbuffer);
        }
        return stringbuffer.toString();
    }


    private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
        char c0 = hexDigits[(bt & 0xf0) >> 4];
        char c1 = hexDigits[bt & 0xf];
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }


    public static boolean checkPassword(String password, String md5PwdStr) {
        String s = getMD5String(password);
        return s.equals(md5PwdStr);
    }


}
